Incubators of test elements provide a key function of maintaining the temperature of the test element and the liquid contained therein, at a desired level, usually an elevated level. The purpose is to render the reaction of the liquid with the reagents of the test element, predictable. Predictability in turn requires that the same temperature be used, more or less, during the several minutes that the reaction needs to "cook". At the same time, a second function that the incubators provide is one of preventing evaporation of the contained liquid, since evaporation can change the amount of analyte being measured, for example, the amount of CO.sub.2 being measured in a potentiometric test element. Because the temperature of the incubator is usually elevated, for example, at 37.degree. C., evaporation will readily occur if the location of the liquid is not covered. Particularly this is true for potentiometric slides such as those described in U.S. Pat. Nos. 4,053,381 and 4,273,639, as in those cases, there is little room for the drops to be absorbed by the test element. That is, the drops tend to protrude above the top of the test element during the entire residence of the test element within the incubator.
Hence, most incubators are provided with evaporation caps, sometimes called covers. These need to seal onto the top of the test element when the latter is in place. Additionally, however, they need to be raised away from the test element as the latter enters into or is removed from the holding means of the incubator. Otherwise, the sealing edges of the cap will "wipe" the excess patient sample protruding above the test element, particularly the potentiometric test element, causing contamination.
One mechanism for effectively placing evaporation caps onto test elements, and for appropriately raising them, is shown in U.S. Pat. No. 4,298,571, FIG. 4. First, the cap has a beveled outside edge that an incoming test element strikes to start raising the cap, when such an element is entering the incubator. However, that alone is not enough to clear the cap from the liquid bubble of the test element, which can be seen in the Figure to protrude above the surface of the test element. In addition, there is provided a push rod that rises up from underneath to lift away the cap (which otherwise is biased against the held test element by spring 104, FIG. 3). That rod in turn is activated by a solenoid (112 in FIG. 4).
Such an incubator is very effective in the kind of large analyzer shown in the '571 patent. However, there has been a need for an incubator using simplified mechanisms, particularly one with a fewer number of active components such as solenoids and motors. Particularly such need is present on small, low-throughout analyzers such as are used in cramped quarters, for example, space stations. That is, the fewer the number of such active components, the smaller and more reliable the incubator can be. This is particularly the case when the cap lifting mechanism is the part that gives the incubator its greatest height, as is apparent from FIG. 5 of the '571 patent.
Analyzers used in space stations to monitor the health of astronauts have an additional constraint--the parts and test elements thereof must be kept confined lest they become floating objects that can be dangerous.
Therefore, prior to this invention there has been a need for an incubator that has means for raising and lowering evaporation caps, which are simplified and take up a minimum of space.